The air stream discharged from the high pressure stage of the compressor of a turbo machine such as a gas turbine engine is directed by a prediffuser to the combustor assembly of the engine. A portion of this high pressure air stream enters the combustor of the engine, and another portion of such stream is directed by the prediffuser into an annular combustor inner passage defined by the combustor inner casing and the inner combustor liner. That portion of the high pressure air stream which flows through the combustor inner passage is utilized to cool the combustor, to provide dilution air into the combustor downstream from the fuel injector thereof and to provide cooling air for the rotor blades of the turbine of the engine.
In many gas turbine engine designs, bleed openings are formed in the aft portion of the combustor inner passage, i.e., substantially downstream from the entrance to the combustor inner passage, and these aft bleed openings provide a path for the flow of high pressure air to the rotor blades of the turbine to cool them. It has been observed that pressure losses are created within combustor inner passages having aft bleed openings due to the formation of a substantial amount of turbulence within the combustor inner passage near its entrance or inlet. It is believed that the high pressure air stream from the compressor enters the inlet to the combustor inner passage and becomes separated into a relatively high velocity stream along the inner combustor liner which forms the outer wall of the combustor inner passage, and a rotating, turbulent air flow along the combustor inner casing which forms the inner wall of the combustor inner passage. This division or separation of the air stream, and the creation of a substantial area of turbulent flow, prevents the air stream from spanning the entire transverse dimension between the inner and outer walls of the combustor inner passage until the air stream travels relatively far downstream from the entrance to the combustor inner passage. By the time the air stream has "filled" or extended itself between the inner and outer walls of the combustor inner passage, pressure losses have been created in such high pressure stream. As a result, the diffusion air from the combustor inner passage flowing into the combustor, and the cooling air flowing out of the aft bleed openings in the combustor inner passage to the turbine rotor blades, are both at pressure levels which are less than desirable and can adversely effect the specific fuel consumption of the gas turbine engine.